1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to video coding and decoding, and more particularly, to video coding and decoding enabling efficient video coding and decoding even when a backward reference path is not permitted because of a low-delay condition, by conducting temporal prediction using the hierarchical temporal filtering method with two or more temporally preceding frames as reference frames.
2. Description of the Related Art
Development of communication technologies including the Internet has led to an increase in video communications in addition to text and voice communications. However, consumers have not been satisfied with existing text-based communication schemes. To satisfy consumer demand, multimedia data containing a variety of information including text, images, music and the like has been increasingly provided. Multimedia data is usually voluminous and it therefore requires a large capacity storage medium. Also, a wide bandwidth is required for transmitting the multimedia data. Under these circumstances, it is necessary to use a compressed coding scheme when transmitting multimedia data.
A basic principle of data compression is to eliminate redundancy in the data. There are three types of data redundancy: spatial, temporal, and perceptual/visual. Spatial redundancy refers to the duplication of identical colors or objects in an image, temporal redundancy refers to little or no variation between neighboring frames in a moving picture frame or successive repetition of the same sound in audio, and perceptual/visual redundancy refers to human inability to perceive high frequencies. By eliminating these redundancies, data can be compressed. Motion compensation-based temporal prediction, a general video coding method, eliminates temporal redundancy.
In temporal prediction, a prediction frame for a current frame to be compressed is generated from one or more neighboring frames, and a residual signal is obtained by subtracting the prediction frame from the current frame. According to temporal levels of a reference frame, temporal prediction is classified into forward prediction, backward prediction, and bi-directional prediction. Forward prediction makes a prediction using a frame that is temporally earlier than the current frame as a reference frame, backward prediction makes a prediction using a frame that is temporally later than the current frame as a reference frame, and bi-directional prediction makes a prediction using a frame that is temporally earlier than the current frame and a frame that is temporally later than the current frame as reference frames.
Among temporal prediction techniques used in the current video coding system, a common one is a temporal filtering method having a hierarchical structure, which conducts temporal prediction based on motion compensation. Bi-directional prediction is a commonly used temporal prediction technique, and it is an important technique for realizing higher coding efficiency.
However, when a backward reference path is restricted because of a low-delay condition, the video coding performance is degraded. Thus, there is a demand for a method to enable temporal prediction by referencing two or more frames even when backward prediction is restricted in temporal prediction by hierarchical temporal filtering.